1. Field of the Invention
In injection systems for direct-injection internal combustion engines, nozzles can be used in which, depending on the stroke length of the nozzle needle in the injector body, a certain number of openings on the nozzle needle tip, which delivers the fuel that is at high pressure to the combustion chambers, are opened or closed. Depending on the vertical position of the nozzle needle in the injector body surrounding it, in lesser quantity a fuel that is at high pressure, depending on the openings that are opened or closed, is injected into the combustion chamber during the preinjection phase, or a greater injection quantity is injected during the main injection phase.
2. Description of the Prior Art
In injection systems for direct-injection internal combustion engines, a preinjection phase and the ensuing main injection phase can be achieved by means of a different vertical stroke length of the nozzle needle in the injector body surrounding it. In injection nozzles whose nozzle needle has a number of bores or openings, some of these openings can be closed by part of the injector body housing by means of how a partial stroke length is set, and after a total stroke of the nozzle needle has been executed relative to the injector body can be opened again, so that upon completion of the total stroke length, all the openings of the nozzle needle tip are opened, and to all these openings, fuel that is at extremely high pressure can be injected into the combustion chambers of an internal combustion engine. Thus during the main injection phase, the nozzle needle can be brought into a vertical stroke position in which fuel reaches the combustion chamber of an engine through all the openings, while on the other hand a partial stroke can also be established in which during the preinjection phase a lesser injection quantity is injected into the combustion chambers of the engine.
To establish the partial stroke length, a stop is required, which keeps the nozzle needle in the injector body, in the position in the valve housing that maintains the partial stroke, during the preinjection phase. A stop realized by mechanical means is exposed to major stresses on material that can lead to premature wear. Premature wear of a mechanical stop face means that an axial play of the nozzle needle will ensue. This can lead to fluctuations in the injection quantity to be injected into the various combustion chambers of the engine, but this injection quantity is defined with extreme precision in the context of a preinjection phase. Fluctuations in the fuel quantity to be injected impair the metering accuracy of an injection nozzle. The wear that occurs can also cause premature failure of the entire injection nozzle unit.
With the version proposed by the invention for creating a hydraulic stop, on the one hand an essentially wear-free adjustment of a partial stroke length of the nozzle needle can be attained, and on the other, by an external opening of the control element that brings about the partial stroke position, the instant when the axial stroke length that defines the partial stroke of the nozzle needle is cancelled can be selected freely.
With the externally actuatable control element provided according to the invention, a flexible adjustment of a graduated opening of a register nozzle can be provided, so that depending on the different degree of openingxe2x80x94dictated by the axial stroke position of the nozzle needlexe2x80x94a controlled uncovering of the openings at the nozzle tip of the nozzle needle can occur.
The external actuation of the control element that accomplishes and defines the partial stroke adjustment of the nozzle needle makes it possible to choose the instant of the partial stroke adjustment of the nozzle needle and also makes it possible to use a 3/2-way control valve for common rail applications, on the control parts of which a vertical motion can be impressed by way of the stressing or unstressing of an outlet-side control part by means of an attendant pressure drop in the control chamber.